Watch for Puddles & Rainbow Patches
The road surface will be the slickest and most dangerous just after the rain has begun. During this time the rain will cause the oil buildup in the pavement to rise to the surface, causing the road surface to essentially become a giant oil slick.
Keep an eye out for little rainbow-edged patches on the street. This is an indication of an oil patch. Never brake or corner in the center of the roadway at intersections, as this is where autos leave the majority of their drippings.
Use Lights
Let everyone know you are there. Heavy rain and the glare from auto headlights reduce motorists' vision, so it is a good idea to ride with a bright LED lamp on the seatpost and handlebar.
Brake Early
A mixture of road grit and water is the fastest method to erode rubber brake pads. Most rims require a full revolution before the brake pads squeegee the water from the braking surface and begin stopping. Plan ahead and brake early.
Use Fenders
If you plan on riding for any length of time, or with others, install fenders on both wheels. It will quadruple your comfort factor and keep your vision crystal clear. It's one of the unspoken rules that on rainy-day group rides you should never show up without fenders.
Be Cautious of Corners
Shift as much of your weight on the outside pedal as possible. Lean your body more than the bike. By doing this, you will be able to corner with a reasonable amount of speed, as the body will tend to remain balanced over the bike when the tires slide over painted lines and unseen oil patches.
